<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .parent {
      background-color: aquamarine;
      /* 边框粗细2像素 样式 实线 */
      border: 2px solid;
      width: 400px;
      height: 250px;
      /* 填充区  */
      padding: 30px;
    }

    .child {
      background-color: deeppink;
      height: 100px;
      /* 边框 */
      border: 2px solid;
    }
  </style>
</head>

<body>
  <div class="parent">
    <div class="child">

    </div>
  </div>
</body>

</html>